Production method of ferrous dihydrogen phosphate

Abstract

The invention discloses a production method of ferrous dihydrogen phosphate, which comprises the following steps of: changing an iron source of iron-process iron phosphate from traditional iron blocks or iron powder into oxide scale, compounding phosphoric acid and sulfuric acid into mixed acid, and controlling the granularity of the oxide scale and the components and acidity of the mixed acid to solve the problems of dissolution and passivation of the oxide scale. According to the method, iron oxide scale can be better dissolved, the residual problem of ferric ions is solved by reducing excessive iron blocks or iron powder, undissolved impurities such as carbon, silicon and iron are removed by filtering, and finally, the stability problem of a reaction system is solved by adjusting the pH value of the system through industrial phosphoric acid and pure water, so that a ferrous dihydrogen phosphate solution required for producing iron phosphate is obtained. The production cost of an iron source required by iron phosphate is greatly reduced, other impurities are not contained, and mixed acid-containing filtrate and washing water generated in the production process can be recycled through an evaporation device.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ferrous phosphate preparation, more particularly, to a ferrous phosphate production method. BACKGROUND

[0002] Ferrous phosphate is an intermediate product for preparing lithium iron phosphate from iron-process iron phosphate. Currently, the iron source of iron-process iron phosphate generally uses pure iron. Compared with the iron source of ammonium-process iron phosphate, which generally uses ferrous sulfate heptahydrate, the cost of iron-process iron phosphate is relatively high. However, in the long run, with the strengthening of environmental protection supervision, the price increase of ferrous sulfate heptahydrate and the saturation of the by-product market, the advantages of iron-process will gradually emerge, and it will certainly become one of the mainstream processes for iron phosphate. Therefore, in order to further improve the market competitiveness of iron-process iron phosphate, it is necessary to further reduce the production cost of iron phosphate, especially the cost of iron source.

[0003] In order to reduce the production cost of iron phosphate, enterprises consider using titanium white or by-products containing iron produced by the steel industry as a substitute for pure iron, which not only realizes the recycling of by-products but also reduces production costs. For example, Chinese patent CN117865088A discloses a method for preparing battery-grade ferrous phosphate solution from titanium slag by-product iron, which comprises the following steps: (1) mixing titanium slag by-product iron with phosphoric acid solution according to the required ratio, and carrying out iron dissolution reaction under inert atmosphere, and then separating the solid and liquid; (2) adding reduced iron powder to the first liquid to adjust the pH to 2-4, and then fully reacting and separating the solid and liquid; (3) adding ammonium salt to the second liquid, fully reacting, and then separating the solid and liquid; (4) adding a flocculating agent to the third liquid, standing, and then separating the solid and liquid to obtain battery-grade ferrous phosphate solution.

[0004] For example, Chinese patent CN116768178A discloses a method for preparing iron phosphate and lithium iron phosphate, which comprises the following steps: adding waste iron scale to an aqueous solution of phosphoric acid, adjusting the pH value, wherein the molar ratio of waste iron scale to phosphoric acid is 1:1.6-2.4, to obtain a ferrous phosphate solution; preparing the ferrous phosphate solution to a predetermined concentration, heating, and adding hydrogen peroxide dropwise to obtain a dihydrate iron phosphate slurry; filtering the dihydrate iron phosphate slurry, and then sintering the filter residue to obtain iron phosphate.

[0005] The above-mentioned prior art uses waste containing elemental iron as the iron source. In order to further reduce the production cost, some enterprises use iron oxide scale containing iron oxide as the iron source. Iron oxide scale is a by-product produced during the steelmaking process, which has high purity and low price, but its main components are Fe2O3, Fe3O4 and FeO, containing a large amount of trivalent iron ions, which is more difficult to handle than iron sources containing elemental iron.

[0006] For example, Chinese patent CN116835546A discloses a method for preparing battery-grade iron phosphate from millscale, which comprises the following steps: (1) mixing dilute phosphoric acid and dilute sulfuric acid in a volume ratio of 1:0.5 to obtain a mixed acid, wherein the mass concentration standards of the dilute phosphoric acid and the dilute sulfuric acid in the mixed acid are as follows: the mass concentration of the dilute phosphoric acid is 20%-40%, and the mass concentration of the dilute sulfuric acid is 1%-3%; (2) adding the mixed acid obtained in step (1) to millscale to obtain a ferrous acid leaching solution I, wherein the acid comprises at least one of sulfuric acid, hydrochloric acid and phosphoric acid; (3) when the reducing property of the metal reducing agent is stronger than that of elemental iron, adding elemental iron to the ferrous acid leaching solution I to carry out a displacement reaction, thereby obtaining a ferrous acid leaching solution II and the metal reducing agent, wherein the metal reducing agent comprises at least one of Zn, Fe and Cu; (4) carrying out impurity removal by neutralization and precipitation on the ferrous acid leaching solution I or the ferrous acid leaching solution II, and then carrying out oxidation and precipitation of iron on the solution after impurity removal; (5) adding ammonium dihydrogen phosphate solid to the solution after impurity removal in a P / Fe molar ratio of 1.05:1, and effectively preventing the co-crystallization process of cationic impurities such as K, Na, Mn, Mg and Ca in the solution by strictly controlling the acidity and reaction temperature and reaction time of the reaction system, so that the cationic impurities are controlled in the solution system and do not co-precipitate with iron ions, thereby obtaining hydrated iron phosphate product; and (6) carrying out a dissolution reaction on the millscale using concentrated sulfuric acid in the method embodiment, which can leach iron in the millscale, but the outermost layer of the millscale is Fe2O3, and the concentrated sulfuric acid has a certain passivation effect on Fe2O3, so that the reaction is incomplete or relatively slow, and the millscale cannot be efficiently and fully utilized.

[0007] In summary, developing a production method for producing ferrous dihydrogen phosphate from a low-cost iron source will greatly reduce the production cost of iron phosphate, and the purity of millscale is high and the price is low, so it is the preferred substitute for iron process pure iron. However, the composition of millscale is complex, and problems such as passivation and the presence of trivalent iron ions in the solution are prone to occur during the dissolution process. Therefore, how to efficiently and fully utilize millscale to obtain a stable ferrous dihydrogen phosphate solution and effectively combine it with the iron process is a problem that needs to be solved without reselecting a new technical route for large-scale investment. SUMMARY

[0008] In view of the above, the present application provides a production method for ferrous dihydrogen phosphate, which changes the iron source of iron process iron phosphate from traditional iron blocks or iron powder to millscale, solves the problems of millscale dissolution and residual trivalent iron ions, and obtains a stable ferrous dihydrogen phosphate solution.

[0009] The present application provides a production method for ferrous dihydrogen phosphate, which comprises the following steps:

[0010] (1) mixing dilute phosphoric acid and dilute sulfuric acid in a volume ratio of 1:0.5 to obtain a mixed acid, wherein the mass concentration standards of the dilute phosphoric acid and the dilute sulfuric acid in the mixed acid are as follows: the mass concentration of the dilute phosphoric acid is 20%-40%, and the mass concentration of the dilute sulfuric acid is 1%-3%;

[0011] (2) adding mixed acid and the oxide scale with the molar ratio of phosphoric acid to iron in the oxide scale being 2-2.5:1, and performing a dissolution reaction under stirring, to obtain a mixed iron ion solution after the reaction is completed;

[0012] (3) adding iron blocks or iron powder to the mixed iron ion solution to perform a reduction reaction, heating the solution after the color of the mixed iron ion solution turns green to perform a dissolution reaction of the remaining iron blocks or iron powder, and obtaining a crude ferrous solution after the reaction is completed;

[0013] (4) performing solid-liquid separation on the crude ferrous solution to obtain a pure ferrous solution;

[0014] (5) adding industrial phosphoric acid and pure water to the pure ferrous solution to obtain a ferrous phosphate solution.

[0015] The mass concentration of the dilute phosphoric acid is 30%-60%, and the mass concentration of the dilute sulfuric acid is 3%-9%.

[0016] The particle size of the oxide scale is ≤15 mm, and a suitable particle size is conducive to solving the passivation problem of the oxide scale. The larger the particle size, the slower the dissolution, and the smaller the particle size, the faster the dissolution.

[0017] In the present application, the dilute sulfuric acid and the dilute phosphoric acid are configured to form the mixed acid to dissolve the oxide scale, which does not bring in chloride ions and other impurity ions affecting the product quality, and has good stability, which is conducive to the stability control of the product.

[0018] In the process of producing ferrous phosphate, phosphoric acid is an essential substance, but the dilute phosphoric acid can cause a passivation reaction of the oxide scale, and the concentrated sulfuric acid also has a passivation effect on the oxide scale, and SO4 2- is not a substance required for the reaction, and the concentration thereof should not be high. Therefore, the dilute sulfuric acid and the dilute phosphoric acid are mixed to avoid the passivation effect of the dilute phosphoric acid on the oxide scale. However, a too high concentration of the dilute sulfuric acid can affect the quality of the subsequent product, and a too high concentration of the dilute phosphoric acid can cause a passivation problem in the subsequent reduction reaction stage. Therefore, in the present application, the mass concentration of the dilute phosphoric acid is controlled to be 30%-60%, the mass concentration of the dilute sulfuric acid is controlled to be 3%-9%, the mass concentration of the dilute phosphoric acid in the mixed acid is controlled to be 20%-40%, and the mass concentration of the dilute sulfuric acid in the mixed acid is controlled to be 1%-3%, which is conducive to avoiding the passivation of the oxide scale and the pH and concentration control of the ferrous phosphate solution in the subsequent production, ensuring the quality of the ferrous phosphate, and reducing the content of SO4 2- .

[0019] Meanwhile, in the present application, the molar ratio of phosphoric acid to iron in the oxide scale is 2-2.5:1 when the mixed acid and the oxide scale are added, the acid is added in excess, so as to ensure the complete dissolution of the soluble components of the oxide scale and the required acidity and acid amount in the subsequent reduction reaction.

[0020] The step (2) is ended when the pH of the solution is less than or equal to 1.5 and the total iron content is 1% to 5%.

[0021] The step (3) is ended when the pH of the solution is 1 to 1.5 and the ferrous content is 5% to 6%.

[0022] The pH and iron content indexes for ending the reaction in the steps (2) to (3) during the reaction process can monitor whether the raw material ratio meets the standard.

[0023] In the step (3), the amount of the iron block or iron powder added in the reduction reaction is 1 to 1.1 times of the theoretical required iron block or iron powder consumption of the ferric ion in the mixed iron ion solution, and the solution is heated to 60 to 80 DEG C after the color of the mixed iron ion solution is changed to green to perform the dissolution reaction of the remaining iron block or iron powder; the amount of the iron block or iron powder is slightly excessive in order to fully convert the ferric ion into ferrous ion, and the unreacted iron block or iron powder can be converted into ferrous ion by reacting with acid, thereby fully utilizing the raw material and solving the residual problem of the ferric ion, and the temperature is controlled at 60 to 80 DEG C in order to accelerate the dissolution reaction of the iron block or iron powder.

[0024] Finally, the pH of the solution is adjusted by industrial phosphoric acid and pure water in order to solve the stability problem of the reaction system, and the pH of the ferrous phosphate solution is 1.1 to 1.4, which can ensure the stability of the subsequent production process of the ferric phosphate.

[0025] The beneficial effects of the present application are as follows:

[0026] (1) The iron source of the iron-process ferric phosphate is changed from the traditional iron block or iron powder to the iron oxide scale, which greatly reduces the production cost of the iron source required by the ferric phosphate;

[0027] (2) The mixed acid is prepared by compounding phosphoric acid and sulfuric acid, and the particle size of the iron oxide scale and the components and acidity of the mixed acid are controlled to solve the problems of the dissolution and passivation of the iron oxide scale, so that the iron oxide scale can be better dissolved and efficiently and fully utilized;

[0028] (3) The residual problem of the ferric ion is solved by using excessive iron block or iron powder for reduction, and no other substances are introduced, and the filtrate and washing water containing the mixed acid generated in the production process can be reused by the evaporation device;

[0029] (4) The process of the present application realizes the low-cost and stable production of ferrous phosphate, and the produced ferrous phosphate can effectively connect the existing iron-process ferric phosphate synthesis device, and has a good popularization prospect. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the flow chart of the production method of ferrous phosphate. DETAILED DESCRIPTION

[0031] Embodiments of the present application will be described in more detail below. The present application can be implemented in various forms and should not be interpreted as being limited to the embodiments set forth herein, which are provided for a more thorough and complete understanding of the present application. It should be understood that the embodiments of the present application are for illustrative purposes only and are not intended to limit the scope of the present application.

[0032] Embodiments of the present application are implemented in the following technical solutions:

[0033] (1) mixing dilute phosphoric acid and dilute sulfuric acid at a volume ratio of 1:0.5 while stirring to obtain a mixed acid, wherein the mass concentration standards of the dilute phosphoric acid and the dilute sulfuric acid in the mixed acid are: the mass concentration of the dilute phosphoric acid is 20% to 40%, and the mass concentration of the dilute sulfuric acid is 1% to 3%, and when the mass concentrations of the dilute phosphoric acid and the dilute sulfuric acid in the mixed acid do not reach the standards, adding dilute phosphoric acid, dilute sulfuric acid or pure water to reach the standard mass concentrations;

[0034] (2) adding the mixed acid and the oxidized iron scale at a molar ratio of phosphoric acid to iron in the oxidized iron scale of 2 to 2.5:1 while starting stirring to perform a dissolution reaction, and when the pH of the solution is 0 to 1.5 and the iron content is 1% to 5%, stopping the dissolution reaction to obtain a mixed iron ion solution;

[0035] (3) adding the trivalent iron ion in the mixed iron ion solution at 1 to 1.1 times the theoretical required iron block or iron powder consumption to a reduction kettle, and then adding the mixed iron ion solution to the reduction kettle to perform a reduction reaction, and when the color of the mixed iron ion solution turns green, heating the solution to 60 to 80°C to perform dissolution of the remaining iron block or iron powder, and when the pH of the solution is 1 to 1.5 and the ferrous content is 5% to 6%, stopping the reaction to obtain a crude ferrous solution;

[0036] (4) performing solid-liquid separation on the crude ferrous solution to obtain a pure ferrous solution;

[0037] (5) adding the pure ferrous solution to industrial phosphoric acid with a mass concentration of 85% and pure water to perform conditioning while starting stirring to perform mixing, and when the pH of the solution is 1.1 to 1.4, stopping the conditioning to obtain the required ferrous dihydrogen phosphate solution.

[0038] Table 1 is the specific implementation conditions of the embodiments of the present application and the pH of the obtained ferrous phosphate solution, wherein the preparation of ferrous phosphate is carried out by using dilute phosphoric acid in the comparative example, because the dissolution of the iron oxide scale in dilute phosphoric acid is poor, resulting in low iron ion content, and finally obtaining a ferrous phosphate solution which does not meet the standard; while through the present application, the iron oxide scale can be well dissolved, and at the same time, qualified ferrous phosphate solution can be obtained, proving the feasibility of the present application, realizing the preparation of stable ferrous phosphate solution by using iron oxide scale as raw material, the iron content and pH value of the prepared ferrous phosphate solution are within 5% to 6% and 1.1 to 1.4, reducing the production cost while ensuring the stability of the subsequent production of iron phosphate.

[0039] Table 1 is the specific implementation conditions of the embodiments of the present application and the pH of the obtained ferrous phosphate solution, wherein the preparation of ferrous phosphate is carried out by using dilute phosphoric acid in the comparative example, because the dissolution of the iron oxide scale in dilute phosphoric acid is poor, resulting in low iron ion content, and finally obtaining a ferrous phosphate solution which does not meet the standard; while through the present application, the iron oxide scale can be well dissolved, and at the same time, qualified ferrous phosphate solution can be obtained, proving the feasibility of the present application, realizing the preparation of stable ferrous phosphate solution by using iron oxide scale as raw material, the iron content and pH value of the prepared ferrous phosphate solution are within 5% to 6% and 1.1 to 1.4, reducing the production cost while ensuring the stability of the subsequent production of iron phosphate.

[0040]

[0041] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any skilled person in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered in the protection scope of the present application, therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for producing ferrous dihydrogen phosphate, characterized in that: The following steps are involved: (1) dilute phosphoric acid and dilute sulfuric acid are mixed in a volume ratio of 1:0.5 to obtain a mixed acid, wherein the mass concentration of the dilute phosphoric acid and the dilute sulfuric acid in the mixed acid is as follows: the mass concentration of the dilute phosphoric acid is 20% to 40%, and the mass concentration of the dilute sulfuric acid is 1% to 3%; (2) adding a mixed acid and iron oxide in a molar ratio of phosphoric acid to iron in iron oxide of 2 to 2.5:1, performing a dissolution reaction under stirring, and obtaining a mixed iron ion solution after the reaction is completed; (3) adding iron block or iron powder to the mixed iron ion solution to carry out a reduction reaction; when the color of the mixed iron ion solution turns green, heating the solution to dissolve the remaining iron block or iron powder; and obtaining a crude ferrous solution after the reaction is completed; (4) performing solid-liquid separation on the crude ferrous solution to obtain a pure ferrous solution; (5) Add industrial phosphoric acid and pure water to the pure ferrous solution to obtain ferrous dihydrogen phosphate solution.

2. A method for producing ferrous dihydrogen phosphate according to claim 1, characterized in that, The mass concentration of the dilute phosphoric acid is 30% to 60%, and the mass concentration of the dilute sulfuric acid is 3% to 9%.

3. A method for producing ferrous dihydrogen phosphate according to claim 1, characterized in that, The particle size of the iron oxide scale is ≤15mm.

4. The method for producing ferrous dihydrogen phosphate according to claim 1, wherein: In step (2), when the pH of the solution is ≤1.5 and the total iron content is 1% to 5%, the dissolution reaction is completed.

5. The method for producing ferrous dihydrogen phosphate according to claim 1, wherein: In step (3), the amount of iron blocks or iron powder added in the reduction reaction is 1 to 1.1 times the theoretical amount of iron blocks or iron powder required for the trivalent iron ions in the mixed iron ion solution.

6. The method for producing ferrous dihydrogen phosphate according to claim 1, wherein: In step (3), after the color of the mixed iron ion solution turns green, the solution is heated to 60-80° C. to perform a dissolution reaction of the remaining iron blocks or iron powder.

7. The method for producing ferrous dihydrogen phosphate according to claim 1, wherein: In step (3), when the pH of the solution is 1 to 1.5 and the ferrous content is 5% to 6%, the dissolution reaction ends.

8. The method for producing ferrous dihydrogen phosphate according to claim 1, wherein: In step (5), the pH of the ferrous dihydrogen phosphate solution is 1.1 to 1.4.

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